The present invention relates to a combined drill and reamer and, more particularly, to a combination tool having in one line a twist drill part and a spiral reamer part.
Referring to FIGS. 1 and 2, conventionally, a drill of rod type C to be adapted for drilling and finishing a hole in a workpiece has hitherto been constructed as a combination of a drill part A at the front portion and a reamer part B at the rear portion, both disposed in a single line as one unit. In the known construction, the drill portion A includes a chisel edge 2 with a drill point 1 and a pair of relieved taps 4 and chip grooves 6 with tap margins 5 therebetween, both of which are formed of spirals in one direction around the axial line of the drill. Also, the reamer portion B includes a pair of reamer cutters 7 and chip flutes 9 with cutter margins 8 therebetween, both of which are formed of spirals in the other direction, opposite to that of the drill portion, with a slanting angle of 4.degree. to 10.degree. with respect to the axial line X of the drill. Therefore, the chip grooves 6 and chip flutes 9 to cross each other, so that the chip pieces of the workpiece cut off by the relieved taps 4 and reamer cutters 7 are sometimes made to block the way for the removal of such chips through the chip grooves 6 and chip flutes 9. In addition thereto, the slanting angle of the reamer cutters 7 is not large enough to produce a cutting force for obtaining a fine finished surface of the hole drilled in the workpiece. Accordingly, on the application of the drill to a workpiece such as 60 mm thick steel plate, the drilled surface of the hole is always provided with a hard roughness, as shown in FIG. 3, resulting in the need for further treatment to finish the surface of hole by the employment of a broach-reamer.